Background: Respiratory distress syndrome (RDS) is one of the most common causes of NICU admission and neonatal death. It is mainly found in premature infants, the risk of developing into RDS increased with decreasing of gestational age and birth weight. Continuous positive airway pressure (CPAP) is a simple, non-invasive, and cost-effective therapy, particularly for preterm neonates with respiratory distress syndrome (RDS). It decreases the need for mechanical ventilation as well as the risks of mortality and bronchopulmonary dysplasia (BPD). The main aim of this study was to assess fraction of Inspired Oxygen as a Predictor of CPAP Failure in preterm with respiratory distress syndrome. Methods: This study enrolled on infant with Respiatroy distress on CPAP.